14 ANATOMY OF THE HORSE. 



AtUerioi' Circumference — Perpendiculaily semi-oval, the small 

 end turned downward ; bounded by the first dorsal vertebra, the 

 first pair of ribs, and the sternum ; making a passage for the 

 trachea, esophagus, longus colli, carotid arteries, jugular veins, 

 vertebral arteries and veins, axillary arteries and veins, par 

 vagum, sympathetic and recurrent nerves, and thoracic duct. 



Posterior Circumference — Wide, but most extensive from 

 above in the antero-inferior direction ; bounded by the last dorsal 

 vertebra, the ensiform cartilage, the two last ribs, and the false 

 cartilages; affording attachment to the abdominal muscles, but 

 more particularly to the diaphragm, by which the intervening 

 space is occupied. 



HI.— THE PELVIS, 



Forms the posterior boundary of the trunk ; is connected 

 with the spine and supported by the femoral bones ; presents a 

 large, irregular cavity, open before and behind, in which are con- 

 tained part of the intestines and the urinary and genital or- 

 gans; and is composed of four bones: — the sacrum and os coc- 

 cygis, and the two ossa innominata. 



THE RUMP-BONE. (oS SACRUM.) 



Situation. At the superior part of the pelvis, continued from 

 the vertebral chain between the ossa ilia. 



Figure. Resembling the lumbar portion of the spine, from 

 which it declines with a slight bend, presenting a convexity 

 externally, a concavity internally, thereby augmenting the area 

 of the pelvic cavity. 



Division. Into two surfaces, two borders, a base, and an 

 apex. 



Superior Surface. Very irregular. Presenting, \st. On the 

 mesian line, five considerable eminences, corresponding to the 

 lumbar spines, from which they differ in sloping in an opposite 

 direction, in increasing in breadth, while they diminish in 

 length, from first to last. 2ndlij. Laterally, two superficial 

 grooves, pierced by the four superior sacral foramina, through 

 which pass out the superior sacral nerves. 



Inferior Surface. Regular, smooth, and slightly concave. It 

 presents — Four transverse lines of demarcation, denoting the 

 original division of the bone into four separate pieces. These 

 are bounded laterally by two superficial grooves, pierced by four 

 pairs of inferior sacral foramina, through which make exit the 

 corresponding sacral nerves. 



